1. Field of the Invention
This invention relates to compositions for personal care formulations, and, more particularly, to a cationic product-structurant composition which forms a bilayer lamellar gel network in an oil-in-water system, thereby to provide a skin feel of lubricity and emollience, skin conditioning, and skin barrier strengthening which brings moisturization to the user without added moisturizer, sun protection through uniform delivery of active sunscreens, and provision of a uniform color from a liquid make-up formulation, as well as effective hair conditioning.
2. Description of the Prior Art
Human body skin forms a barrier which protects the body against uncontrolled loss of water. The outermost layer of the skin, the stratum corneum, provides this barrier. Traditionally, the stratum corneum has been described as a bricks-and-mortar structure in which the corneocyte xe2x80x9cbricksxe2x80x9d are surrounded by lipid xe2x80x9cmortarxe2x80x9d. The lipid region is known to provide the semi-permeability barrier needed for healthy skin, and the physical organization of the lipids is known to be critical for good barrier function.
Skin lipids have been the subject of much research in recent years, and the relatively simple xe2x80x9cmortarxe2x80x9d model has recently evolved into a more complex xe2x80x9cDomain Mosaic Modelxe2x80x9d (DMM). In this model, skin lipids are described as having domains of solid or gel-state lipids bordered by lipids in a more fluid liquid crystalline state called a xe2x80x9cgrain boundaryxe2x80x9d.
A DMM arrangement provides an effective barrier that prevents the indiscriminate loss of water, yet allows controlled evaporation to regulate body temperature. The more fluid character of the grain boundaries represents areas where materials may diffuse in or out of the system. However, any loss of lipid can disrupt the barrier function of the stratum corneum. Healthy skin thus requires optimal barrier function and maintenance of skin moisture for prevention of irritation and dryness.
Lipid loss can arise due to excess washing, exposure to cold and dry climates, or dietary unbalance. Lipid depletion eventually causes a weakened, more permeable barrier which readily loses moisture, resulting in rough, dry skin. A permeable barrier also is more readily penetrated by foreign materials which can cause effect adverse reactions in sensitive skin.
Lipids may be replenished by topical application of a skin care formulation. However, it is crucial that such lipids be present therein in suitable form if barrier function is to be rapidly restored, preferably in a bilayer lamellar gel network which approximate the structure of lipids within the stratum corneum. Such bilayer lamellar gel networks also can provide product-structuring of oil-in-water emulsions by formation of multilayer vesicles with the oil phase and extended bilayer sheets throughout the water phase which eliminates the need for application of conventional emulsifiers that do not provide any benefit to the skin.
Conner et al in U.S. Pat. No. 4,012,398, described an emollient composition having hair conditioning properties which was the reaction product of mink oil, dimethylaminopropylamine and enchlorohydrin. However, the unsaturated fatty acids present in mink oil have been found to be unsatisfactory for lamellar gel networks.
Accordingly, it is an object of this invention to provide a cationic skin conditioning agent, and product-structuring or emulsion compositions therewith, in the form of a cationic bilayer lamellar gel network which approximates the natural structure of the stratum corneum lipids and is stable to temperatures up to 80xc2x0 C., wherein the cationic (negative charged) lamellar gel is strongly attracted to human skin, so that the charge interaction between the skin and the lamellar gel provides excellent skin coverage, effective skin conditioning, and long-lasting barrier enhancement.
Yet another object herein is to provide skin care formulations including such cationic bilayer lamellar gel network compositions and resulting emulsion formulations, having a skin feel of lubricity and emollience, and which provides moisturization without added moisturizer, and which can deliver active sunscreens to the skin surface by the cationic bilayer lamellar gel network system thus providing excellent, long-lasting photoprotection.
A particular object herein is to provide product-structuring or emulsion compositions and skin care formulations therewith whose skin feel is moist and substantive in their skin feel after use.
These and other objects and features of the invention will be made apparent from the following description.
What is described herein is a product-structuring composition which will form a bilayer lamellar gel network in an oil-in-water system comprising (a) a cationic swellant which is a fatty acid adduct of amidopropyldimethyl-2-hydroxyethyl ammonium halide, and (b) a gellant blend of low HLB emulsifiers having a resultant HLB of about 1.5 to 4.5.
Preferably the composition includes a saturated fatty acid such as stearic or palmitic acid, or mixtures thereof, suitably present in an amount, by weight, of about 0.5 to 5% of the composition and (b) being the remainder 100%.
Preferably (b) includes a group of emulsifiers having a non-ionizable group selected from fatty alcohols and esters, optionally with an ionizable emulsifier which is a fatty acid, particularly wherein said fatty alcohol is behenyl alcohol and said fatty ester is glycerol stearate or sorbitan monostearate, or mixtures thereof, in a weight ratio of fatty ester to fatty alcohol of about 2:1 to about 1.6:1, and the weight ratio of saturated fatty acid emulsifier to (a) is about 2:1 to about 4:1.
A preferred composition is wherein (b) comprises by weight, about 30-60% glycerol stearate, about 25-50% cetyl alcohol, about 3-8% behenyl alcohol and about 2-8% of a mixture of palmitic and stearic acids.
Also described herein are personal care formulations having about 2-8% of the product-structuring composition, such as skin care, hair conditioning and sunscreen formulations.